1. Field of the Invention
The invention relates to a radio system, in particular a mobile radio system.
2. Description of the Related Art
The recent sharp increase in the number of mobile radio subscribers and the provision of new services in mobile radio have caused mobile radio networks, such as the GSM network for example, to approach the limits of their capacity. As is known, in the GSM network, traffic channels are used for the transmission of user data and signalling channels are used for the control and management of a mobile radio network. However, the signalling load in a mobile radio network is very high, since information has to be constantly exchanged over the air interface, even when no connection has been set up between a base station and a mobile station. An important signalling channel is represented here by the so-called broadcast control channel, also known as the BCCH channel, over which for example radio channel configurations, synchronizing information and identifications for registration are sent to all the mobile stations of a cell. Such a BCCH channel may take up as much as half of the available frequency spectrum of a cell, which is then of course no longer available for traffic channels. To allow better utilization of the spectrum reserved for a cell, it is generally known to subject the individual traffic channels when need be to a frequency hopping process, in which the carrier frequency for a traffic channel is changed at a predetermined regular rate. The frequency hopping process cannot be used, however, for a BCCH channel, since the BCCH channel is required for measurements of the receiving field strength and selection of the strongest cell. This has the result that the distance between cells in which the same BCCH carrier frequency is being used is much greater than the distance between cells in which the same traffic carrier frequency is being used. For example, the cluster size for a BCCH channel of a GSM network is 12 to 21 cells, whereas for traffic channels a cluster size of 3 to 9 cells is entirely adequate. The cluster size is understood here as meaning the number of cells among which the available frequencies are divided.
However, there have previously been no proposed ways of making more efficient use of the available carrier frequencies for signalling channels in the manner possible with the aid of the frequency hopping process for traffic channels.